Summary On the morning of 04 March 2004, the ro-ro passenger ferry Caribou departed Port aux Basques, Newfoundland and Labrador, on a regularly scheduled six-hour crossing to North Sydney, Nova Scotia. At about 1620, approximately 14nautical miles from the North Sydney terminal, a series of furnace explosions occurred in the starboard auxiliary boiler. The resulting fires were quickly extinguished and the Caribou completed its voyage. One of two officers who suffered burns was airlifted to Halifax, Nova Scotia, for special medical treatment. Ce rapport est galement disponible en franais. Other Factual Information Particulars of the Vessel Description of Vessel Photo1.Ro-ro passenger and vehicle ferry Caribou The Caribou was built in 1985as a roll on-roll off (ro-ro) ferry to transport passengers and vehicular traffic between Nova Scotia and Newfoundland. Vehicles are carried on decks1 and3, and passenger facilities are on decks3 through7. The vessel can accommodate 1313passengers, and 370automobiles or 77tractor trailers, and may have a crew of up to 87personnel. History of the Voyage At 11302 on 04 March 2004, the ro-ro passenger ferry Caribou with 23passengers, 3cadets, 4Marine Atlantic employees and 70crew departed on a scheduled crossing from Port aux Basques, Newfoundland, to North Sydney, Nova Scotia. The first two hours of the voyage were uneventful. Three propulsion engines were on line prior to the occurrence. Photo 2 - Starboard auxiliary boiler At 1340, the machinery alarm and monitoring system (AMS) detected a flame failure (flame-out) in the starboard auxiliary heating boiler. The boiler was reset, and a restart was attempted, but the burner failed to light. The second engineer checked the fuel filters and finding one dirty, replaced it. The pilot burner assembly was then removed and, suspecting the fuel nozzle to be dirty, the existing 2.5gallon-per-hour (gph) nozzle was also removed and replaced with a spare one rated at 2gph. The pilot burner assembly was re-installed and a restart attempted. Once again the burner failed to light. The pilot burner assembly was withdrawn and a series of tests were carried out to confirm the presence of an ignition spark and to assess the quality of the fuel nozzle spray pattern. The spray pattern was good, but the spark appeared weak, which required adjusting the ignition electrodes. With the assembly reinstalled, another restart proved unsuccessful. The pilot burner assembly was withdrawn. Soon afterwards, the chief engineer, who had originally gone to the machinery control room to pick up the log book, was informed of the boiler problems. He immediately proceeded to the starboard boiler to assist the second engineer. The senior chief electrical officer, who was passing through the engine room, also stopped to assist. The second engineer left to look for a spare replacement fuel nozzle, while the chief engineer and senior chief electrical officer carried out the same checks that had already been performed. During these checks it was discovered that one of the electrodes was grounding out. A spare fuel nozzle could not be located, but a new set of electrodes was installed, adjusted, and a boiler restart attempted. Again the boiler failed to ignite. After removing the pilot burner, it was found that one of the electrodes had shifted. The electrode was readjusted, and the pilot burner was re-installed, but the unit failed to start. After one more unsuccessful set of checks and adjustments, the decision was made to fire the boiler in the emergency running mode. One, possibly two, failed attempts were made at firing the boiler using this procedure. At approximately 1620, the chief and second engineers went to the machinery control room away from the noise to discuss the problem, while the senior chief electrical officer went to the port boiler to compare the settings of the two units. When the chief and second engineers arrived at the machinery control room , they heard a loud bang. A cloud of black smoke was seen forming in the starboard forward section of the engine room. The chief engineer went to the boiler, while the second engineer started the fire pump. The wheelhouse was informed of the situation, the engine room fans were shutdown, and the main propulsion engines were then slowed to idle. The resulting fire on the starboard boiler at the time of the first explosion was quickly extinguished using a portable extinguisher. The chief engineer and senior chief electrical officer were both standing in the general vicinity of the starboard boiler when a second explosion occurred. The chief engineer suffered burns from the explosion, and he retreated to an adjacent compartment. The senior chief electrical officer also received burns while extinguishing the ensuing fire. Shortly thereafter, a third explosion occurred, and the fire was fought using portable extinguishers and foam. The main power to the starboard boiler was then turned off. Meanwhile, the emergency fire party arrived to counter any flare-ups, and the first-aid team attended to injuries. At 1630, the fire was declared out. The engine room ventilation fans were restarted, and a fourth main propulsion engine was brought on line. At 1645, the vessel got underway, arriving at the North Sydney terminal at1749. The Caribou was met by Emergency Health Services personnel, and the two injured personnel were transferred to hospital for treatment. (See AppendixA - Sketch of the Occurrence Area.) Injuries to Crew The senior chief electrical officer suffered second-degree burns to his left hand and wrist, while the chief engineer suffered various first-, second- and third-degree burns to his legs, torso, arms, and face. Damage to the Vessel and Environment Damage was confined to the starboard auxiliary boiler. The four securing dogs on the boiler burner assembly door were sheared off. The main and pilot burner tubes, as well as the tertiary air register, were dislodged. The linkage to the main burner air regulator was severed, and the fire bricks lining the floor of the boiler were severely disturbed. Electrical wiring aft of the starboard boiler suffered fire and heat damage. There was no damage to the ocean environment. Vessel Certification The Caribou was crewed, certificated, and equipped to existing regulations. The vessel is classed Lloyd's100A1, and has an ice class, 1ASuper. It is subject to regular inspection under Transport Canada (TC) as a Passenger Ship (non-convention) and was last issued a Safety Inspection Certificate (SIC16) on 04February2004, valid until 15April2004. The starboard auxiliary boiler is subject to bi-annual inspection and was last surveyed by TC in April2002. The vessel held valid International Safety Management (ISM)3 certification issued by Lloyd's Register of Shipping. Personnel Certification The master and officers of the Caribou were certificated for the class of vessel and its type of voyage. All of the officers and crew had Marine Emergency Duties training. Personnel History The master had 31years experience with Marine Atlantic Inc. and served approximately 16years as master on various vessels in the company's fleet. The chief engineer had approximately 22years sea experience and 9years as chief engineer. This was his second trip on the Caribou. The second engineer had been employed by Marine Atlantic since June2002 with four-months experience on the Caribou. The senior chief electrical officer had been employed on the Caribou for 16years. Weather Winds were from the north west at 22to 33knots with wave heights estimated at 1to 2metres. The air temperature was -3C. Passenger/Vehicle Manifest The passenger manifest indicated that 13passengers, 10truck drivers, 13tractor-trailers, and 22drop-trailers (no tractors attached) were on board the vessel. Auxiliary Boilers Description of the Starboard Auxiliary boiler The starboard auxiliary boiler is a SUNROD CPH-120 vertical cylinder, oil-fired steam boiler. It is equipped with a NU-WAYQF3 burner head that is supplied air from both primary and secondary fans. The burner has a control system that regulates the burner either in a fully automatic or in a semi-automatic operation. The duration of the boiler purge4 was set at 30seconds. The boiler is also fitted with all mandatory safety devices, which include, but are not limited to, steam pressure cut-in/-out, low water level lock-out, and flame failure lock-out. Although capable of using heavy fuel, both boilers are fired exclusively using marine diesel oil. The boilers' main fuel supply comes from a ring-main system, and both units also share a common fuel supply for their respective pilot burners that is independent of the main fuel oil supply. The working pressure of the main fuel oil supply is 3bar, while the working pressure for the pilot burner oil supply is 7bar. Photo 3 - Primary and secondary fans Combustion air is supplied partly as primary air through the burner itself, and partly as secondary and tertiary air that is introduced through the metal head of the burner. The primary fan5 is a high-pressure, low-volume unit, while the secondary fan6 is a low-pressure, high-volume unit. Approximately 90percent of the combustion air is delivered directly to the burner casing through the two dampers for the secondary and tertiary air. The remaining 10percent of the combustion air is passed to the primary .air fan that further raises the pressure of the air so that it will provide sufficient energy to atomize the fuel oil.7 The primary fan also supplies combustion air to the pilot burner assembly (see Photo3). History of the Starboard Boiler On or about 23 February 2004, the primary fan motor on the starboard auxiliary boiler suffered an electrical failure and was sent ashore for repairs. Thereafter, the port auxiliary boiler was in service, with the starboard unit being kept warm on standby. However, at approximately 1130on 01March2004, the burner unit on the port boiler suffered a mechanical problem that necessitated putting the starboard boiler back into service even though it was still missing the primary air fan. The fan from the port boiler was not transferred to the starboard boiler. History of the Port Boiler On 11 August 1997, the port auxiliary boiler suffered a similar furnace explosion that required renewal of the burner unit. The explosion was attributed to fuel oil pooling in the main burner tube and air supply chambers.8 There were no reported injuries in that occurrence. Burner Operation In automatic operation, the burner automatically starts and stops on a signal from the steam pressure switch. A regulating motor is mechanically connected to the fuel modulating valve, air dampers, and inner air cone, and controls the fuel-air ratio (firing rate) according to steam demand. If the boiler flames out while in operation, the burner will lock out to prevent an unauthorized restart. In semi-automatic operation, the burner automatically starts and stops on a signal from the steam pressure switch, but the boiler only fires at a fixed firing rate, independent of boiler steam demand. The firing rate is adjusted by manually operating the regulating motor and, thereby, increasing or decreasing the fuel and air flow to the burner unit. As with the fully-automatic operation, if the boiler flames out while in operation, the burner will lock out to prevent an unauthorized restart. Alarm and Monitoring System The main and auxiliary machinery, including both auxiliary heating boilers, are monitored by an alarm and monitoring system (AMS). When a monitored parameter falls outside a predetermined range, the alarm system detects the abnormality and enters an alarm state. Nine boiler points are monitored by the AMS, including flame/ignition failure. Each time a boiler suffers an uncommanded flame failure, the event registers on the AMS. Typically, most AMSs .are fitted with data-logging printers to assist with troubleshooting or with determining the series of events. The AMS onboard the Caribou is capable interfacing with a printer, but none was fitted. Fuel Oil Pressures The boiler fuel pressures recorded after the occurrence were Main Burner Fuel Oil Pressure- 2bar and Pilot Burner Fuel Oil Pressure- 2.5bar. Emergency Operation In the event that the automatic oil burner control fails, the boiler can be fired in an emergency mode of operation using a keyed switch (see Photo4). Unlike firing the boiler using the oil burner control, all steps essential to firing the boiler are carried out manually, and all safety devices, including the flame monitoring device, are bypassed. When the chief and second engineers left the starboard auxiliary boiler, the main power switch was left in the ONposition, the emergency running switch was in the automatic position, and the hand-auto switch was either in the automatic or in the manual position. Furnace Explosions General Minor furnace explosions are often referred to as flashbacks or blowbacks. The basic cause of a furnace explosion is the ignition of an accumulated combustible mixture within the confined space of the furnace/combustion chamber. The flammable mixture within this enclosure consists of an accumulated quantity of combustibles that, when mixed with air in the correct proportions between the upper and lower explosive limits,9 will result in rapid and uncontrolled combustion when an ignition source is applied. The size and intensity of the explosion depend largely on the quantity of combustibles and the fuel-to-air ratio at the time of ignition. Secondary Explosions When a primary explosion occurs within a contained space, the resulting damage may allow air to be drawn into the partial vacuum created by the rapid combustion/explosion. The primary explosion can result in a secondary explosion by disrupting,10 dispersing, and igniting new sources of fuel. Secondary explosions can be considerably more destructive than the primary explosion, and every primary explosion may cause several secondary explosions. Photo 5 - Internal damage to starboard auxiliary boiler The force of the explosions was greater than the boiler burner assembly door could withstand; the four securing dogs were sheared off, and the burner door was partially opened. The force of the blast also dislodged the main and pilot burner tubes, and the tertiary air register, and severed the linkage to the main burner air regulator. It was also of sufficient magnitude to disturb the fire bricks lining the floor of the boiler (see Photo5). Uniform and Protective Clothing The chief engineer was wearing a polyester-cotton short-sleeve dress shirt and polyester-wool pants. This was his normal on duty, supervisory attire. The senior chief electrical officer wore a dress uniform similar to that worn by the chief engineer, but supplemented by a polyester-wool battle dress jacket and a polyester safety vest. The second engineer was wearing coveralls.11 The clothing worn by all three individuals was provided by Marine Atlantic. None of these items were treated to enhance flame-retardant properties. The uniform shirt and pants worn by the chief engineer were extensively burned or melted by contact with the flame front from the second explosion. The back of the pants, safety vest, and battle jacket worn by the senior chief electrical officer caught fire and burned through as a result of the third explosion. Marine Atlantic Uniform Issue The uniform and protective clothing issued to Marine Atlantic employees is manufactured from a variety of fabrics, whose fibre content ranges from 100 per cent natural fibres to 100 per cent synthetic fibres and includes numerous fibre blends. None of the clothing issued by the company, other than the rain gear, was treated to enhance flame-retardant properties (see AppendixB - Marine Atlantic Uniform Issue). Flammability Characteristics of Various Fabrics Fabrics are manufactured from natural or manufactured fibres, or a combination of the two. Natural fibres are produced from either plants (cellulose) or animals (protein). Manufactured fibres are produced by combining simple compounds (monomers) to form more complex compounds or polymers. Each fibre, whether natural or manufactured, has its own unique durability and flammability characteristics. Fabrics made from cellulose fibres tend to be more durable, but exhibit poor flammability characteristics. Fabrics produced from protein fibres, on the other hand, are less durable, but demonstrate good flammability properties. Manufactured synthetic fabrics, although durable, are generally heat sensitive. Modern textiles are often produced by combining natural and manufactured fibres to obtain the flammability properties of one and the durability characteristics of the other.12 Laundering Practices and Flame Resistance Improper laundering can degrade the flammability characteristics of fabrics with natural flame-resistant properties, as well as those treated with flame-resistant chemicals. Failing to follow the manufacturer's washing instructions, or even using liquid fabric softener, can seriously alter a fabric's flame-resistant properties. Regulatory Requirements The marine requirements for uniform/protective clothing are referenced in the Marine Occupational Safety and Health Regulations13 and the Safe Working Practices Regulations.14 The regulations, however, offer no guidance as to what fabrics may constitute suitable uniform/protective clothing. Although not applicable to the marine industry, parallels can be drawn from a Transport Canada System Safety Air Carrier Advisory Circular, which informed air operators of the potential hazards when uniforms issued to flight attendants do not provide adequate protection in situations involving fire or emergency evacuations.15